Metal surface treatment composition, metal surface treatment method, and galvanized steel plate

ABSTRACT

It is an object of the present invention to provide a metal surface treatment composition and a metal surface treatment method superior in stability, which can apply a good chemical conversion treatment to a galvanized steel plate without requiring a burden of waste water treatment, and a galvanized steel plate superior in a rust-preventive property and adhesion, which is obtained by such a metal surface treatment method. A metal surface treatment composition comprising niobium oxide colloidal particles, wherein the niobium oxide colloidal particles are derived from a niobium oxide sol which is stabilized by containing citric acid or salts thereof in an amount of 0.02 to 1.0 by a mole ratio relative to Nb.

TECHNICAL FIELD

The present invention relates to a metal surface treatment composition,a metal surface treatment method and a galvanized steel plate.

BACKGROUND ART

Galvanized steel plates, to which zinc plating or zinc alloy plating isapplied, are used as steel materials having the high corrosionresistance. In such galvanized steel plates, a zinc plating layer isoxidized through contact with air to form white color rust. Therefore,it is necessary to prevent oxidation by applying surface treatment. Insome applications, galvanized steel plates are used without being coatedafter being processed. In such a case, it is important that thegalvanized steel plate has a rust-preventive property in an uncoatedcondition.

As such treatment, there is known chromate-treatment using a chromiumcompound. When chromate-treatment is applied, the formation of whitecolor rust is prevented and a very good galvanized steel plate can beobtained. However, since the waste water containing a chromium compoundrequires a great deal of burden for the disposal, a method of performingchemical conversion treatment with a chromate-free treatment agent notusing chromium is studied.

As such a chromate-free treatment agent, there are disclosed metalsurface treatment agents for galvanized steel plates, which containmetal salt compounds (cf. Japanese Kokai Publication Hei-9-241856,Japanese Kokai Publication 2001-172771 and Japanese Kokai Publication2001-247977, for instance). However, galvanized steel plates, surfacetreated with such the treatment agents, did not have sufficientproperties of a rust-preventive property, adhesion to a film and thelike.

In addition, a chemical conversion treatment solution for galvanizedsteel plates, which contains oxyacid salts of metals selected frommolybdenum, vanadium, tungsten, niobium and tantalum, manganesecompounds, titanium compounds and phosphoric acid or phosphates, isdisclosed (cf. Japanese Kokai Publication 2002-105659, for instance).However, in such a chemical conversion treatment solution for galvanizedsteel plates, it is necessary to use a manganese compound. Since themanganese compound also requires a great deal of burden for the disposalof its waste water, it is preferred not to use it.

In addition, as a rust-preventive component used for a metal surfacetreatment composition, water-dispersible silica is used. However, whenthe water-dispersible silica is used alone, it did not have an adequaterust-preventive property and the metal surface treatment compositioncould not attain an adequate rust-preventive property in providing therust-preventive property for such a galvanized steel plate.

SUMMARY OF THE INVENTION

In view of the above circumstances, it is an object of the presentinvention to provide a metal surface treatment composition and a metalsurface treatment method superior in stability, which can apply a goodchemical conversion treatment to a galvanized steel plate withoutrequiring a burden of waste water treatment, and a galvanized steelplate superior in a rust-preventive property and adhesion, which isobtained by such a metal surface treatment method.

The present invention provides a metal surface treatment compositioncomprising niobium oxide colloidal particles,

-   -   wherein the niobium oxide colloidal particles are derived from a        niobium oxide sol which is stabilized by containing citric acid        or salts thereof in an amount of 0.02 to 1.0 by a mole ratio        relative to Nb.

Preferably, the niobium oxide colloidal particle has an average particlediameter of 100 nm or less.

Preferably, the niobium oxide colloidal particle has a content of 1 mass% or more relative to the total nonvolatile matter in the metal surfacetreatment composition when Nb contained in the niobium oxide colloidalparticle is converted to equivalent Nb₂O₅.

Preferably, the metal surface treatment composition comprises

-   -   a water-borne resin in an amount of 5 to 90 mass % relative to        the total nonvolatile matter in the metal surface treatment        composition.

Preferably, the water-borne resin is at least one kind selected from thegroup consisting of acrylic resin, polyolefinic resin, polyurethaneresin, epoxy resin, olefin-acrylic acid copolymer resin, phenolic resin,polyester resin, alkyd resin, melamine resin, polycarbonate resin,polyacrylic acid and copolymers or block polymers thereof.

Preferably, the metal surface treatment composition comprises

-   -   water-dispersible silica in an amount of 80 mass % or less        relative to the total nonvolatile matter in the metal surface        treatment composition.

Preferably, the metal surface treatment composition comprises

-   -   at least one compound selected from the group consisting of        vanadium compounds, zirconium compounds and titanium compounds        in an amount of 0.1 to 30 mass % on the V, Zr or Ti basis        relative to the total nonvolatile matter in the metal surface        treatment composition.

Preferably, the metal surface treatment composition comprises

-   -   a silane coupling agent in an amount of 0.5 to 30 mass %        relative to the total nonvolatile matter in the metal surface        treatment composition.

Preferably, the metal surface treatment composition comprises

-   -   a phosphate compound in an amount of 0.1 to20 mass % relative to        the total nonvolatile matter in the metal surface treatment        composition.

Preferably, in the metal surface treatment composition, pH is 6 to 11.

Preferably, in the metal surface treatment composition, theconcentration of the nonvolatile matter is 3 to 50 mass % on the mass ofthe nonvolatile matter basis.

The present invention provides a metal surface treatment methodcomprising

-   -   applying surface treatment to a galvanized steel plate with the        metal surface treatment composition, thereby forming a coat        thereof.

The present invention provides a coated galvanized steel plate obtainedby the metal surface treatment method.

DISCLOSURE OF THE INVENTION

Hereinafter, the present invention will be described in detail.

A metal surface treatment composition of the present invention comprisesa niobium oxide sol which is formed by dispersing niobium oxidecolloidal particles highly stabilized with citric acid or salts thereofin an aqueous medium. The niobium oxide colloidal particles morepreferably have a smaller average particle diameter because when theaverage particle diameter is small, a more stable and dense treated coatof the niobium oxide is formed and therefore the niobium oxide colloidalparticles can provide a rust-preventive property stably for an articleto be treated. In addition, the metal surface treatment composition doesnot need to contain components, requiring a burden of waste watertreatment, such as chromium and manganese.

The niobium oxide colloidal particle to be used in the present inventionrefers to one which is formed by niobium oxide dispersing in fineparticle form in water. For example, a substance, which is present inintermediate region between niobium hydroxide and niobium oxide andbecomes an amorphous state without becoming complete niobium oxide, maybe used.

The metal surface treatment composition of the present invention can beprepared by using a niobium oxide sol made by a method publicly known.The niobium oxide sol is not particularly limited, and for example, asubstance made by a publicly known method, which is described inJapanese Patent No. 2849799 and the like, can be given. Further, niobiumoxide sol made by Taki Chemical Co., Ltd. may be employed.

An example of a method of producing the niobium oxide sol may include amethod in which niobium oxide is dissolved in hydrofluoric acid and thedissolved solution is added to aqueous ammonia and then the mixture isfiltered and washed to yield niobium hydroxide in slurry form, andoxalate dihydrate is added to the slurry of niobium hydroxide and thenwater is added, and after a uniform solution composed of niobium oxidecolloidal particles is obtained by allowing the reaction of this mixtureto proceed under stirring in a condition of refluxing, then citric acidor salt thereof was added to the solution and the resulting mixture isstirred. In order to adjust the obtained niobium oxide sol to a desiredlevel of pH, a basic compound such as ammonia may be added to the sol asrequired. In order to identify that the reaction has been completed,that is, a uniform solution of niobium oxide colloidal particles hasbeen obtained before adding citric acid, color of the slurry solutioncan be utilized and when the slurry exhibits blue color, it is assumedto be in a uniform state.

The niobium oxide sol, which can be used for the metal surface treatmentcomposition of the present invention, is formed by making the niobiumoxide sol solution stabilized with oxalic acid further contain citricacid and highly stabilizing it. The metal surface treatment compositionof the present invention can be prepared by diluting the niobium oxidesol to a required concentration or by adding another component asrequired and is stable over the long term without causing thickening,gelation or precipitation even after the preparation. An essential pointis that the niobium oxide sol to be used in the metal surface treatmentcomposition of the present invention is in a state highly stabilizedwith citric acid or salt thereof, and an amount of oxalic acid or saltthereof, which is mixed in producing the niobium oxide sol, is notparticularly limited. The niobium oxide sol is preferred in thatthereby, the stability of niobium oxide colloidal particles is notdegraded in being mixed with another components, which is contained inthe metal surface treatment composition of the present invention, suchas a water-borne resin, water-dispersible silica, vanadium compounds,zirconium compounds, titanium compounds, silane coupling agents and thephosphate compounds.

An amount of citric acid or salts thereof added to the metal surfacetreatment composition of the present invention is preferably within arange of 0.02 (lower limit) to 1.0 (upper limit) by a mole ratiorelative to Nb in the metal surface treatment composition. When theamount of citric acid or salts thereof to be added is less than 0.02 bya mole ratio, the stability in adding another components becomesinsufficient, and when it exceeds 1.0 by a mole ratio, it is notpossible any longer to attain an effect of stabilization correspondingto the amount to be added and hence it is uneconomical.

The niobium oxide colloidal particles preferably have an averageparticle diameter of 100 nm or less. When the average particle diameteris small, the niobium oxide colloidal particles can provide arust-preventive property stably for an article to be treated because amore stable and dense treated coat of the niobium oxide is formed. Theaverage particle diameter of the niobium oxide colloidal particles canbe measured using a particle size distribution analyzer based on dynamicscattering light, for example, NICOMP MODEL-370 type (manufactured byPACIFIC SCIENTIFIC INSTRUMENTS Co.).

The metal surface treatment composition of the present inventionpreferably contains the niobium oxide colloidal particles in an amountof 1 mass % or more relative to the total nonvolatile matter in themetal surface treatment composition when Nb in the colloidal particlesis converted to equivalent Nb₂O₅. When the content is less than 1 mass%, it is not preferred since a sufficient rust-preventive propertycannot be attained. The lower limit of the content is more preferably 2mass %, furthermore preferably 3 mass %. The upper limit is preferably30 mass %, more preferably 15 mass %.

Further, the metal surface treatment composition of the presentinvention preferably comprises a water-borne resin. A water-borne resinused herein is one containing a water-soluble resin and awater-dispersible resin. The water-borne resin is not particularlylimited, and examples thereof may include acrylic resins, polyolefinicresins, polyurethane resins, epoxy resins, olefin-acrylic acid copolymerresins, phenolic resins, polyester resins, alkyd resins, melamineresins, polycarbonate resins and polyacrylic acid, and another thermallycrosslinking type and thermoplastic type resins.

These water-borne resins may be used alone or in combination of two ormore species, or in the form of copolymers or block polymers thereof.When the water-borne resin is used, a leveling agent, a wetting agentand an antifoaming agent may be used in order to improve a film formingproperty and form a more uniform and smooth film.

When the metal surface treatment composition of the present inventioncomprises the water-borne resin, the content of the water-borne resin ispreferably within a range of 5 mass % (lower limit) to 90 mass % (upperlimit) relative to the total nonvolatile matter in the metal surfacetreatment composition. When the content exceeds 90 mass %, it is notpreferred since the adding effect will saturate in this range and theaddition becomes uneconomical. When it is less than 5 mass %, it is notpreferred since the rust-preventive property may deteriorate. The lowerlimit is more preferably 10 mass %, furthermore preferably 20 mass %.The upper limit is more preferably 80 mass %, furthermore preferably 70mass %.

Preferably, the metal surface treatment composition of the presentinvention further comprises water-dispersible silica in order to improvethe rust-preventive property of a surface treatment film. Thewater-dispersible silica cannot attain an adequate rust-preventiveproperty when it is used alone, but it can improve the rust-preventiveproperty multiplicatively by being used in combination with the niobiumoxide colloidal particles.

The water-dispersible silica is not particularly limited, and examplesthereof may include spherical silica, chain silica and aluminum-modifiedsilica, which have fewer impurities such as sodium and the like. Thespherical silica is not particularly limited, and examples thereof mayinclude colloidal silica such as “SNOWTEX N”, “SNOWTEX O”, “SNOWTEX OXS”and “SNOWTEX UP” (each made by Nissan Chemical Industries, Ltd.) andfumed silica such as “AEROSIL” (made by Nippon Aerosil Co., Ltd.). Thechain silica is not particularly limited, and examples thereof mayinclude silica sol such as “SNOWTEX PS-M” and “SNOWTEX PS-MO” (each madeby Nissan Chemical Industries, Ltd.). Examples of the aluminum-modifiedsilica may include commercially available silica gel such as “ADELITEAT-20A” (made by Asahi Denka Co., Ltd.)

When the metal surface treatment composition of the present inventioncomprises the water-dispersible silica, the content of SiO₂ in the metalsurface treatment composition is preferably 80 mass % or less relativeto the total nonvolatile matter in the metal surface treatmentcomposition. When the content exceeds 80 mass %, there is a problem thata coat becomes brittle and a rust-preventive property deteriorates. Theupper limit is more preferably 60 mass %, furthermore preferably 30 mass%.

Preferably, the metal surface treatment composition of the presentinvention further comprises at least one compound selected from thegroup consisting of vanadium compounds, zirconium compounds and titaniumcompounds in order to improve the rust-preventive property of a surfacetreatment film. It is possible to further improve the rust-preventiveproperty by using the niobium oxide colloidal particles in combinationwith the at least one compound selected from the group consisting ofvanadium compounds, zirconium compounds and titanium compounds. It ismore preferred to use four, five or six components of the niobium oxidecolloidal particles, the water-borne resin, the water-dispersiblesilica, and the at least one compound selected from the group consistingof vanadium compounds, zirconium compounds and titanium compounds incombination.

The vanadium compound, zirconium compound and titanium compound are notparticularly limited as long as they are water-soluble orwater-dispersible compounds, and specific examples thereof are asfollows.

The vanadium compound is not particularly limited, and examples thereofmay include vanadyl compounds, vanadium pentoxide, vanadates, burnedpolyvanadic acid, heteropoly vanadic acid and mixtures thereof. Specificexamples thereof may include vanadium (II) compounds such as vanadium(II) oxide, and vanadium (II) hydroxide; vanadium (III) compounds suchas vanadium (III) oxide (V₂O₃); vanadium (IV) compounds such as vanadium(IV) oxide (V₂O₄), and vanadyl halides (VOX₂); vanadium (V) compoundssuch as vanadium (V) oxide (V₂O₅); vanadates such as variousorthovanadates, metavanadates or pyrovanadates, vanadyl halides (VOX₃);or mixtures thereof. Vanadates are not particularly limited, andexamples thereof may include ammonium salt, alkaline metal salts,alkaline earth metal salts (for example, magnesium, calcium), metalsalts of another typical elements (for example, aluminum, tin) andtransition metal salts (for example, manganese, cobalt, iron, nickel).In particular, alkaline earth metal salts, zinc salt, manganese salt,and cobalt salt are preferred. These may be obtained by burning oxidesof vanadium and oxides, hydroxides or carbonates of various metalstogether at a temperature of 600° C. or more.

The zirconium compound is not particularly limited, and examples thereofmay include fluorozirconic acid (H₂ZrF₆); ammonium, lithium, sodium, orpotassium salts of fluorozirconic acid; ammonium zirconate oxycarbonate((NH₄)₂ZrO (CO₃)₂); zirconate compounds such as zirconium hydroxide,zirconium carbonate, zirconium borate, zirconium oxalate, zirconiumsulfate, zirconium nitrate, zirconyl nitrate, and zirconium fluoride;organic zirconate compounds such as dibutylzirconium dilaurate,dibutylzirconium dioctate, zirconium naphthenate, zirconium octylate,and acetylacetone zirconium; or mixtures thereof.

The titanium compound is not particularly limited, and examples thereofmay include fluorine-titanium compounds such as fluorotitanic acid,ammonium fluorotitanate, sodium fluorotitanate, potassiumfluorotitanate, fluorotitanic acid, alkaline metal fluorotitanate, andtitanium fluoride; organic titanium compounds such as titanium potassiumoxalate, titanium isopropoxide, isopropyl titanate, titanium ethoxide,titanium 2-ethyl 1-hexanolate, tetraisopropyl titanate, tetran-butyltitanate, butyltitanate dimer, titanium lactate, and titaniumtriethanolaminate; or mixtures thereof.

When the metal surface treatment composition of the present inventioncomprises at least one compound selected from the group consisting ofthe vanadium compounds, the zirconium compounds and the titaniumcompounds, the content of the compounds is preferably within a range of0.1 mass % (lower limit) to 30 mass % (upper limit) on the V, Zr or Tibasis relative to the total nonvolatile matter in the metal surfacetreatment composition. When the content exceeds 30 mass %, it is notpreferred since the adding effect will saturate in this range and theaddition becomes uneconomical. When it is less than 0.1 mass %, it isnot preferred since the rust-preventive property may deteriorate. Thelower limit is more preferably 0.5 mass %, furthermore preferably 1.0mass %. The upper limit is more preferably 15 mass %, furthermorepreferably7.5 mass %. Incidentally, since some kinds of compounds to beused may cause the gelation and thickening of the metal surfacetreatment composition and the solution stability may deteriorate, it isnecessary to blend the compounds within a preferred range.

Preferably, the metal surface treatment composition of the presentinvention further contains a silane coupling agent. It is preferred inthat by containing the silane coupling agent, the adhesion of a coat toa metal surface can be improved and the silane coupling agent has anaction as a crosslinking agent of the water-borne resin and thereby thecorrosion resistance can be improved. The silane coupling agent is notparticularly limited, and examples thereof may includevinylmethoxysilane, vinyltrimethoxysilane, vinylethoxysilane,vinyltriethoxysilane, 3-aminopropyltriethoxysilane,3-glycidoxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane,3-mercaptopropyltrimethoxysilane,N-(1,3-dimethylbutylidene)-3-(triethoxysilyl)-1-propane amine,N,N′-bis[3-(trimethoxysilyl)propyl]ethylenediamine,(N-β-aminoethyl)-γ-aminopropylmethyldimethoxysilane,(N-β-aminoethyl)-γ-aminopropyltrimethoxysilane,γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane,γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane,γ-glycidoxypropylmethyldimethoxysilane,2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,γ-methacryloxypropyltrimethoxysilane,γ-methacryloxypropyltriethoxysilane, γ-mercaptopropyltrimethoxysilane,γ-mercaptopropyltriethoxysilane andN-[2-(vinylbenzylamino)ethyl]-3-aminopropyltrimethoxysilane.

Among them, examples of the particularly preferred silane coupling agentmay include vinylmethoxysilane, vinylethoxysilane,3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane,3-methacryloxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilaneand N-(1,3-dimethylbutylidene)-3-(triethoxysilyl)-1-propane amine,N,N′-bis[3-(trimethoxysilyl)propyl]ethylenediamine. The silane couplingagent may be used alone or in combination of two or more species.

When the metal surface treatment composition of the present inventioncomprises the silane coupling agent, the content of the silane couplingagent in the metal surface treatment composition is preferably within arange of 0.5 mass % (lower limit) to 30 mass % (upper limit) relative tothe total nonvolatile matter in the metal surface treatment composition.When the content of the silane coupling agent is less than 0.5 mass %,it is not preferred since the effect of improving corrosion resistanceand adhesion to a chromium-free rust-preventive coating agent may beinsufficient, and when it exceeds 30 mass %, it is not preferred sincethe adding effect will saturate in this range and the addition becomesuneconomical, and in addition the gelation and thickening of thecomposition may arise and the solution stability may deteriorate. Thelower limit is more preferably 1 mass % and the upper limit is morepreferably 20 mass %.

The metal surface treatment composition of the present inventionpreferably contains a phosphate compound. The phosphate compoundcontained in the metal surface treatment composition of the presentinvention has a function of further improving the rust-preventiveproperty of a surface treatment film by eluting metal, being a materialto be treated, and forming a metal salt of phosphate on the surface ofthe material to be treated.

The phosphate compound is not particularly limited as long as it is acompound capable of forming phosphate ions in water, and examplesthereof may include phosphorous acid, hypophosphorous acid, organicphosphoric acids, organic phosphorous acids, phosphoric acid; phosphatesalts such as Na₃PO₄, Na₂HPO₄ and NaH₂PO₄; and polyphosphoric acid suchas polyphosphoric acid, metaphosphoric acid, pyrophosphoric acid andultraphosphoric acid, and salts thereof.

When the metal surface treatment composition of the present inventioncomprises the phosphate compound, the content of the phosphate compoundin the metal surface treatment composition is preferably within a rangeof 0.1 mass % (lower limit) to 20 mass % (upperlimit) relative to thetotal solid matter in the metal surface treatment composition. When thecontent is less than 0.1 mass %, it is not preferred since the effect ofimproving the corrosion resistance may be insufficient, and when itexceeds 20 mass %, it is not preferred since this may cause excessiveetching on a galvanized steel plate or the gelation of the composition.The lower limit is more preferably 0.5 mass % and the upper limit ismore preferably 10 mass %.

The metal surface treatment composition of the present inventionpreferably has pH within a range of 6 (lower limit) to 11 (upper limit).When the pH is less than 6, the stability in mixing the niobium oxidesol may deteriorate and the solution stability of the whole compositionsmay deteriorate, and in addition this pH may cause excessive etching ona galvanized steel plate to lead to a defective appearance. When itexceeds 11, it is not preferred since this pH may cause excessiveetching on a galvanized steel plate to lead to a defective appearance.The lower limit is more preferably 7 and the upper limit is morepreferably 10. The pH of the metal surface treatment composition ispreferably adjusted within the range by adding a basic compound.Particularly, it is more preferred to use volatile compounds such asammonia and amines as the basic compound.

The metal surface treatment composition of the present inventionpreferably contains nonvolatile matter within a range of 3 mass % (lowerlimit) to 50 mass % (upper limit) on-the mass of the nonvolatile matterbasis. When the concentration of the nonvolatile matter is less than 3mass %, it is not preferred since it may be impossible to attain ansufficient film thickness for maintaining the rust-preventive propertyin applying the metal surface treatment composition. When it exceeds 50mass %, it is not preferred since this may cause the gelation of thecomposition. The lower limit is more preferably 10 mass % and the upperlimit is more preferably 30 mass %.

The niobium oxide colloidal particles highly stabilized by the citricacid or salts thereof to be used in the present invention also has theexcellent stability in mixing with such electrolyte components asdescribed above. Therefore, the metal surface treatment composition ofthe present invention, which comprises the respective componentsdescribed above, is superior in the stability, so that it can performthe surface treatment of a galvanized steel plate with stability.

A method of producing the metal surface treatment composition of thepresent invention is not particularly limited, and it can be obtained,for example, by charging the niobium oxide colloidal particles, thewater-borne resin, the water-dispersible silica, at least one compoundselected from the group consisting of vanadium compounds, zirconiumcompounds and titanium compounds, the silane coupling agent and thephosphate compound to a container in this order and by stirring theresulting mixture so as to become uniform.

The metal surface treatment method of the present invention is a methodin which a galvanized steel plate is treated with the metal surfacetreatment composition. A galvanized steel plate, which can be treated inthe metal surface treatment method of the present invention, is notparticularly limited, and examples thereof may include steel plates,which are plated with zinc or a zinc-based alloy through electroplating,hot dipping and vacuum evaporation coating, such as a galvanized steelplate, a steel plate plated with a zinc-nickel alloy, a steel plateplated with a zinc-iron alloy, a steel plate plated with a zinc-chromiumalloy, a steel plate plated with a zinc-aluminum alloy, a steel plateplated with a zinc-titanium alloy, a steel plate plated with azinc-magnesium alloy and a steel plate plated with a zinc-manganesealloy.

In the metal surface treatment method, the galvanized steel platedegreased as required is treated with the metal surface treatmentcomposition. The treating method with the metal surface treatmentcomposition is not particularly limited, and examples thereof mayinclude roller coating, shower coating, air-spray coating, airless-spraycoating, curtain flow coating, brush coating and immersion coating,which are commonly used.

Preferably, the metal surface treatment composition of the presentinvention is applied in an application rate of 0.1 g/m² (lower limit) to10.0 g/m² (upper limit) as amass of the nonvolatile matter in a coat.When this application rate is less than 0.1 g/m², there may be caseswhere the ability to be processed deteriorates or the rust-preventiveproperty is not adequately attained due to insufficient thickness. Whenit exceeds 10.0 g/m², there may be cases where it is economicallydisadvantageous since there is not an increase in the effect ofincreasing a film thickness or winding becomes difficult due to theincreased thickness. The lower limit is more preferably 0.2 g/m², andfurthermore preferably 0.3 g/m². The upper limit is more preferably 5.0g/m², and furthermore preferably 3.0 g/m².

It is preferred to dry the coat by heating after treating with the metalsurface treatment composition. A temperature, at which the drying isconducted, is preferably within a range of 50° C. (lower limit) to 250°C. (upper limit). When it is less than 50° C., drying efficiency maybecome worse due to a low evaporation rate of water. When it exceeds250° C., formed components in a coat may be decomposed due to elevatedtemperatures. More preferably, the lower limit is 60° C. and the upperlimit is 150° C. Drying time is preferably in a rage of 1 second (lowerlimit) to 300 seconds (upper limit), and more preferably in a rage of 3seconds (lower limit) to 60 seconds (upper limit).

The present invention also provides a galvanized steel plate obtained bythe metal surface treatment method. Since the galvanized steel plate ofthe present invention is one on which a good surface treatment coat isformed, it has an excellent rust-preventive property and does not formwhite color rust.

The metal surface treatment composition of the present invention is onewhich comprises the niobium oxide colloidal particles having theexcellent stability and provides the galvanized steel plate with thegood rust-preventive property and adhesion equal to a chromate-treatmentagent without requiring a burden of waste water treatment. By using themetal surface treatment composition, it is possible to provide themethod of metal surface treatment, which can apply a good metal surfacetreatment to a galvanized steel plate. Further, by using the method ofmetal surface treatment of the present invention, it is possible toprovide a galvanized steel plate which has the excellent rust-preventiveproperty and adhesion.

Since the metal surface treatment composition of the present inventionincludes the niobium oxide colloidal particles highly stabilized withcitric acid or salts thereof, it has the excellent solution stabilityand provides the good rust-preventive property and adhesion for a filmto be obtained. Further, since the metal surface treatment compositionof the present invention does not contain components such as chromiumand manganese as an essential component, it does not require anexcessive burden of waste water treatment.

EXAMPLES

Hereinafter, the present invention will be described in detail by way ofexamples, but the present invention is not limited to these examples. Inaddition, “%” refers to “mass %” in the examples, unless otherwisespecified.

Preparation of Metal Surface Treatment Compositions Examples 1 to 16,and Comparative Examples 1 to 3

Charged To a container were water-dispersible silica, a vanadiumcompound, a zirconium compound, a titanium compound, niobium oxidecolloidal particles, a water-borne resin, a silane coupling agent and aphosphate compound in this order under being stirred. After stirring for30 minutes, deionized water was added to this mixture to prepare metalsurface treatment compositions having the composition shown in Table 1.Concentrations of the nonvolatile matter and pHs of the obtained metalsurface treatment compositions are shown in Table 2.

Comparative Example 4

A metal surface treatment composition having the composition shown inTable 1 was prepared by following the same procedure as in Example 15except for changing the niobium oxide colloidal particles to K₂NbF₇(made by Morita Chemical Industries Co., Ltd.), which is a solubleniobium compound. A concentration of the nonvolatile matter and pH ofthe obtained metal surface treatment composition is shown in Table 2.

The niobium oxide colloidal particles, the water-borne resins, thewater-dispersible silica, the vanadium compounds, the zirconiumcompounds, the titanium compounds, the silane coupling agents and thephosphate compounds used in Table 1 were as follows.

[Niobium Oxide Colloidal Particle]

A: niobium oxide sol (Nb₂O₅: 10%, average particle diameter: 5 nm, pH 4,citric acid/niobium (mole ratio)=0, made by Taki Chemical Co., Ltd.)

B: niobium oxide sol SAM-02 (Nb₂O₅: 10%, average particle diameter: 5nm, pH 3.8, citric acid/niobium (mole ratio)=0.05, made by Taki ChemicalCo., Ltd.)

C: niobium oxide sol SAM-04 (Nb₂O₅: 5%, average particle diameter: 10nm, pH 9, citric acid/niobium (mole ratio)=0.16, made by Taki ChemicalCo., Ltd.)

[Water-Borne Resin]

A: PC 2200 (ethylene-acrylic acid copolymer resin, concentration ofnonvolatile matter: 30%, made by SHOEI CHEMICAL CO., LTD.)

B: SUPERFLEX 420 (polyurethane resin, concentration of nonvolatilematter: 32%, made by DAI-ICHI KOGYO SEIYAKU CO., LTD.)

C: JURYMERAC-10L (polyacrylic acid, concentration of nonvolatile matter:40%, made by NIHON JUNYAKU CO., LTD.)

[Water-Dispersible Silica]

A: SNOWTEX O (SiO₂: 20%, made by Nissan Chemical Industries, Ltd.)

B: ADELITE AT-20A (SiO₂: 20%, made by Asahi Denka Co., Ltd.)

C; SNOWTEX N (SiO₂: 20%, made by Nissan Chemical Industries, Ltd.)

[Vanadium Compound]

A: ammonium metavanadate (V: 43.6%, reagent)

B: vanadium pentoxide (V: 56.0%, reagent)

C: sodium metavanadate (V: 41.8%, reagent)

[Zirconium Compound]

A: Zircosol AC-7 (zirconium ammonium carbonate, Zr: 74.0% (on the solidmatter basis), made by DAIICHI KIGENSO KAGAKU KOGYO CO., LTD.)

B: (acetylacetonato) zirconium (IV) (Zr: 18.7%, reagent)

[Titanium Compound]

A: Orgatics TC-400 (titanium triethanolaminate, Ti: 10.4% (on the solidmatter basis), made by Matsumo to Chemical Industry Co., Ltd.)

[Silane Coupling Agent]

A: Sila-Ace S-510 (γ-glycidoxypropyltrimethoxysilane, concentration ofnonvolatile matter: 100%, made by CHISSO CORPORATION)

B: Sila-Ace S-210 (vinyltrimethoxysilane, concentration of nonvolatilematter: 100%, made by CHISSO CORPORATION)

[Phosphate Compound]

A: diammonium hydrogen phosphate (concentration of nonvolatile matter:100%, reagent) TABLE 1 Metal surface treatment composition (mass %relative to the total nonvolatile matter) Water- Niobium oxide colloidalparticles Water-borne dispersible Vanadium Zirconium Mole ratio of resinsilica compound compound Kinds Mass % citric acid pH Kinds Mass % KindsMass % Kinds Mass % Kinds Mass % Example 1 C 100 0.16 9.0 — — — — — — —— 2 C 30 0.16 9.0 A 70 — — — — — — 3 B 30 0.05 3.8 A 70 — — — — — — 4 C30 0.16 9.0 A 40 C 30 — — — — 5 C 1 0.16 9.0 A 70 B 29 — — — — 6 C 100.16 9.0 A 30 A 60 C 10 (V: 4.2) — — 7 C 10 0.16 9.0 A 30 C 59 — — A 1.0(Zr: 0.7) 8 C 10 0.16 9.0 B 30 C 55 — — A 5.0 (Zr: 3.7) 9 C 1 0.16 9.0 A90 C 8.8 B 0.2 (V: 0.1) — — 10 C 10 0.16 9.0 C 10 C 42 — — A 38 (Zr:28.1) 11 C 20 0.16 9.0 A 55 C 5 — — B 20 (Zr: 3.7) 12 C 10 0.16 9.0 A  5A 80 A 5.0 (V: 2.2) — — 13 C 5 0.16 9.0 A 65 A 20 C 10 (V: 4.2) — — 14 C7 0.16 9.0 A 65 A 24 A 2.0 (V: 0.9) — — 15 C 7 0.16 9.0 A 64 A 24 A 2.0(V: 0.9) — — 16 C 7 0.16 9.0 A 63 A 24 A 2.0 (V: 0.9) — — Comparative 1— — — — A 70 A 28 A 2.0 (V: 0.9) — — Example 2 — — — — A 70 A 24 A 2.0(V: 0.9) — — 3 A 10 0 4.0 A 30 A 50 A 10 (V: 4.4) — — 4 K₂NbF₇:16(Nb₂O₅: 7) C 64 A 15 A 2.0 (V: 0.9) — — Metal surface treatmentcomposition (mass % relative to the total nonvolatile matter) TitaniumSilane Phosphate compound coupling agent compound Kinds Mass % KindsMass % Kinds Mass % Example 1 — — — — — — 2 — — — — — — 3 — — — — — — 4— — — — — — 5 — — — — — — 6 — — — — — — 7 — — — — — — 8 — — — — — — 9 —— — — — — 10 — — — — — — 11 — — — — — — 12 — — — — — — 13 — — — — — — 14A 2.0 (Ti: 0.2) — — — — 15 A 2.0 (Ti: 0.2) A 1.0 — — 16 A 2.0 (Ti: 0.2)B 1.0 A 1.0 Comparative 1 — — — — — — Example 2 A 2.0 (Ti: 0.2) A 1.0 A1.0 3 — — — — — — 4 A 2.0 (Ti: 0.2) A 1.0 — —Preparation of Test Panels

Commercially available galvanized steel plates (manufactured by NipponTestpanel Co., Ltd., 70 mm×150 mm×0.4 mm) were degreased by spraying at60° C. for 2 minutes using SURF CLEANER 53S (made by NIPPON PAINT Co.,Ltd.), being a commercially available alkaline degreasing agent, andrinsed with water and dried. After drying the steel plates, the metalsurface treatment compositions prepared in Examples 1 to 16 andComparative Examples 1 to 4 were applied to the steel plates with abarcoater in such a way that an application rate after drying was 0.2 to1.0 g/m² of surface area and then dried at a metal surface temperatureof 80° C. to obtain test panels. The resulting test panels wereevaluated according to the following methods. The results ofmeasurements are shown in Table 2. The application rate was given byanalyzing metal elements in the composition using “XRF-1700” (X-rayfluorescence spectrometer manufactured by Shimadzu Corp.) to yield thecontents by mass % of metal elements relative to total nonvolatilematter and converting the content.

(Evaluation Methods)

<Corrosion Resistance>

A flat portion of each test panel and an end face and a rear face of aformed portion, which was extruded by 8 mm by an Erichsen tester, ineach test panel were sealed with a tape and 5% salt water was sprayed tothe coated surface of the test panel at 35° C. After a lapse of 72 hourssince salt water spray, a rate of the surface area where white colorrust was generated was evaluated according to the following criteria.

-   ⊚: no white color rust occurred-   ◯: less than 10% ratio of the surface area where white color rust    occurred-   ◯Δ: not less than 10% and less than 30% of that ratio-   Δ: not less than 30% and less than 50% of that ratio-   ×: not less than 50% of that ratio    <Film Appearance>

The appearance of the test panels was visually evaluated according tothe following criteria. TABLE 2 Concentration of Corrosion resistancenonvolatile (SST 72 hours) matter in pH of Portion formed treatmenttreatment Application Flat by Erichsen Film Solution composition (%)composition rate (g/m²) portion tester Appearance stability Examples 1 59.0 1.0 ◯Δ ◯Δ ⊚ ⊚ 2 10 8.7 0.8 ◯ ◯ ⊚ ⊚ 3 5 6.0 0.8 ◯ ◯ ◯ ◯ 4 10 8.6 0.8⊚ ◯ ⊚ ⊚ 5 10 9.0 0.8 ◯ ◯Δ ⊚ ⊚ 6 10 8.4 0.4 ⊚ ⊚ ⊚ ⊚ 7 10 8.6 0.6 ⊚ ◯ ⊚ ⊚8 5 8.6 0.4 ⊚ ⊚ ⊚ ⊚ 9 10 8.7 0.6 ◯ ◯ ⊚ ⊚ 10 5 8.4 0.6 ⊚ ⊚ ⊚ ◯ 11 5 8.40.5 ⊚ ⊚ ⊚ ⊚ 12 5 7.8 0.6 ⊚ ◯ ⊚ ⊚ 13 10 8.4 0.4 ⊚ ⊚ ⊚ ◯ 14 20 8.4 0.4 ⊚ ⊚⊚ ⊚ 15 20 8.4 0.3 ⊚ ⊚ ⊚ ⊚ 16 20 8.4 0.2 ⊚ ⊚ ⊚ ⊚ Comparative 1 15 8.5 0.8Δ X ⊚ ⊚ Examples 2 15 8.5 0.4 Δ Δ ⊚ ⊚ 3 5 4.0 0.4 ⊚ ⊚ Δ X 4 7 3.0 0.4 ΔΔ X Δ

As shown in Table2, the metal surface treatment compositions obtained inExamples 1 to 16 were superior in the solution stability and the filmsobtained by applying the metal surface treatment compositions had thehigh corrosion resistance and the good appearances. On the other hand,since the metal surface treatment compositions obtained in ComparativeExamples 1 and 2 could not attain chemical conversion coats which hadexcellent rust-preventive property, they could not obtain goodgalvanized steel plates. In addition, the metal surface treatmentcomposition obtained in Comparative Example 3 was not good in thesolution stability and the appearance of the obtained film was inferiorto that of Examples. Further, the metal surface treatment composition ofComparative Example 4, not containing the niobium oxide colloidalparticles, exhibited thickening of solution by secular changes and theappearance and the corrosion resistance of the obtained film were notsatisfactory.

1. A metal surface treatment composition comprising niobium oxidecolloidal particles, wherein the niobium oxide colloidal particles arederived from a niobium oxide sol which is stabilized by containingcitric acid or salts thereof in an amount of 0.02 to 1.0 by a mole ratiorelative to Nb.
 2. The metal surface treatment composition according toclaim 1, wherein the niobium oxide colloidal particle has an averageparticle diameter of 100 nm or less.
 3. The metal surface treatmentcomposition according to claim 1 or 2, wherein the niobium oxidecolloidal particle has a content of 1 mass % or more relative to thetotal nonvolatile matter in the metal surface treatment composition whenNb contained in the niobium oxide colloidal particle is converted toequivalent Nb₂O₅.
 4. The metal surface treatment composition accordingto claim 1 or 2, comprising a water-borne resin in an amount of 5 to 90mass % relative to the total nonvolatile matter in the metal surfacetreatment composition.
 5. The metal surface treatment compositionaccording to claim 4, wherein the water-borne resin is at least one kindselected from the group consisting of acrylic resin, polyolefinic resin,polyurethane resin, epoxy resin, olefin-acrylic acid copolymer resin,phenolic resin, polyester resin, alkyd resin, melamine resin,polycarbonate resin, polyacrylic acid and copolymers or block polymersthereof.
 6. The metal surface treatment composition according to claim 1or 2, comprising water-dispersible silica in an amount of 80 mass % orless relative to the total nonvolatile matter in the metal surfacetreatment composition.
 7. The metal surface treatment compositionaccording to claim 1 or 2, comprising at least one compound selectedfrom the group consisting of vanadium compounds, zirconium compounds andtitanium compounds in an amount of 0.1 to 30 mass % on the V, Zr or Tibasis relative to the total nonvolatile matter in the metal surfacetreatment composition.
 8. The metal surface treatment compositionaccording to claim 1 or 2, comprising a silane coupling agent in anamount of 0.5 to 30 mass % relative to the total nonvolatile matter inthe metal surface treatment composition.
 9. The metal surface treatmentcomposition according to claim 1 or 2, comprising a phosphate compoundin an amount of 0.1 to 20 mass % relative to the total nonvolatilematter in the metal surface treatment composition.
 10. The metal surfacetreatment composition according to claim 1 or 2, wherein pH is 6 to 11.11. The metal surface treatment composition according to claim 1 or 2,wherein the concentration of the nonvolatile matter is 3 to 50 mass % onthe mass of the nonvolatile matter basis.
 12. A metal surface treatmentmethod applying surface treatment to a galvanized steel plate with themetal surface treatment composition according to claim 1 or 2, therebyforming a coat thereof.
 13. A coated galvanized steel plate obtained bythe metal surface treatment method according to claim 12.